Manly officials say they never had any concerns about the use of supplements by players while sports science guru Steve Dank was involved with the club.

Dank's role in Essendon's controversial fitness program will come under scrutiny during an investigation by the AFL and Australian Sports Anti-Doping Authority into the Bombers' use of potentially illegal substances. Dank recently left the AFL club.

It has been alleged Essendon players were asked to sign waivers relating to treatment they were receiving, while club officials said ''questions had been raised'' about supplements given to players last season.

Dank, who was in charge of the Bombers' sports science program, had previously been employed by the Sea Eagles for six years - including in 2008 when they won the premiership.

It was during Dank's time at the club that Fairfax Media revealed the use of calves' blood by some Manly players to aid recovery. Under Dank's guidance, Manly also introduced DNA testing of players, GPS tracking to monitor their performances and the use of radical herbal supplements such as the $300-per-litre anti-inflammatory product Lact-Away, which is made from the bark of French pine and was initially a racehorse treatment.

He left to join Essendon in 2011 and Sea Eagles officials said they never had any concerns during his time with the club. ''Steve was employed as a consultant between 2006 and 2010. During that time, we never had any concerns,'' Manly football manager Steve Gigg said. ''We always complied with all anti-doping protocols of the WADA code and the NRL.''

The NRL is expected to follow the Essendon case closely but does not outlaw supplements for players.

''Everyone is always looking for an edge but the players need to realise that if they take a product that contains a banned substance, they will go. They are ultimately responsible for themselves,'' one official told Fairfax Media.

Essendon face scrutiny over supplements supplied to their players last year. While the Bombers are confident performance-enhancing drugs (PEDs) are not involved, ASADA will lead the joint investigation with the AFL.

The investigation is understood to centre on the possibility Essendon players were injected with peptides or ''related substances'' and that they were asked to sign consent forms handed to them by some of the conditioning staff.

There are various types of peptides, including those which promote muscle growth and thus have similar properties to human growth hormone. There are also peptides that are inert and legal for athletes to take.

Essendon have admitted its players took supplements but the club leadership said they only learnt in recent days that there were issues with some of these products. The club would not say how many of its players had taken these supplements.

While the AFL is working with ASADA, any potential punishment could be out of the AFL's hands as it would be required to fall in line with ASADA policy. The AFL will rely heavily on ASADA's expertise in the matter and a source said the AFL would be in accord with the drug agency in terms of punishment. Players could face bans of more than two years if found guilty of using performance-enhancing drugs.

Former Essendon player Kyle Reimers told Channel Nine that the club knew it was pushing the boundaries with its program. ''From what they were saying, it was right on the borderline of what they were going to give us,'' he said. ''Everyone signed it, it was a personal choice as to whether they took it ... it does seem very odd the type of stuff we were taking. They admitted to us it was right on the edge of the levels you could be taking.''

Ashen-faced Essendon chairman David Evans, coach James Hird and chief executive Ian Robson on Tuesday said the club knew players took supplements but had only discovered information in the previous 24-48 hours that was ''slightly concerning'' about the substances and immediately contacted the AFL.

The AFL community has been abuzz since last season with reports that Essendon players were using ''unorthodox'' substances. Various media outlets including Fairfax Media had repeatedly asked Essendon - including as late as Monday evening - about the claims and were given strenuous denials.

Hird said he believed the players were clean. ''The supplements our players were given, in my knowledge, were all approved and within the regulations we all play the game by,'' he said. ''I'm very disappointed - shocked is probably the best word.''